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Topic: A/C Compressor Question  (Read 1012 times) previous topic - next topic

A/C Compressor Question

My a/c suddenly quit cooling. I checked and noticed the compressor clutch was not engaging. There is a red and black wire on top of the compressor that disappears behind the pulley. I'm assuming this is a signal wire to engage the clutch. I'm also assuming that this wire is most likely fused. My question is this. Should the red wire have 12 volts? And if it doesn't, does anyone have any idea where I might start looking for a fuse on an 08' Nimbus 342?  I'm on the road and like a dummy I left my Foretravel  box with all my schematics at home. Thanks.
2008 Nimbus 342
Build# 6464
ISM 500
Allison 4000 w/retarder
2021 Jeep Grand Cherokee

Re: A/C Compressor Question

Reply #1 –
If you are low on Freon the clutch won't engage.
Peter and Frieda Morin
1999 36ft. U320 Foretravel
Build # 5436
1998 Suzuki Sidekick Sport

Re: A/C Compressor Question

Reply #2 –
Quote from: oldguy –
If you are low on Freon the clutch won't engage.
I hope that's not the case. I had it repaired at MOT June 21 when I bought it. They leaked checked it and found none. I guess anything is possible. I was hoping something simple. 😂
2008 Nimbus 342
Build# 6464
ISM 500
Allison 4000 w/retarder
2021 Jeep Grand Cherokee

Re: A/C Compressor Question

Reply #3 –
Many AC vehicle systems have a sensor that shuts down the compressor with high engine temps. It could be bad. Possible switch on that allows the blower to circulate air without the compressor being on. Have member with same coach send you the fuse and relay number and location to check.

Pierce

Pierce and Gaylie Stewart
'93 U300/36 WTBI
Detroit 6V-92TA Jake
1140 watts on the roof
SBFD (ret)

Re: A/C Compressor Question

Reply #4 –
You are in luck. I have just got done working on my dash AC and almost have the schematic memorized.  I have it attached.  For
 the compressor to work the control module sends a ground to the clutch relay and the power relay.  When the clutch relay is activated it sends 12 volts back to the engine where there are 2 sensors on the freon line.  I believe one is a high limit and the other is a low limit. If all is good then 12v is sent to the compressor. 

First test is to take a test light and see if you have 12v at the compressor. If no 12 V then look for the two sensors that are attached to the freon lines. If no go there then the problem may be under the dash with the AC control module or a relay.

If one of the sensors on the freon line are open, then either a freon problem or bad sensor
2014 ih45  (4th Foretravel owned)
 1997 36' U295 Sold in 2020, owned for 19 years
  U240 36' Sold to insurance company after melting in garage fire
    33' Foretravel on Dodge Chassis  Sold very long time ago

Re: A/C Compressor Question

Reply #5 –
Quote from: turbojack –
  I believe one is a high limit and the other is a low limit. If all is good then 12v is sent to the compressor. 
One limit switch (I believe the high pressure) is located near the compressor, the other one on my coach is located near the condenser.  When my compressor quit working it only required me to disconnect the sensor wire, clean it and replug it.  That saved me replacing a sensor.  Hope yours is the same. 

Richard
Jan & Richard Witt
1999 U-320  36ft WTFE
Build Number: 5478 Motorcade: 16599
2011 Jeep Wrangler Unlimited w/Air Force One
Jan: NO5U, Richard:KA5RIW
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Re: A/C Compressor Question

Reply #6 –
You can hot wire the compressor and check the clutch .  The clutch has an air gap  that gets larger with age and can be adjusted to function at least once in its life.
  After  checking the above electrical functions.

Re: A/C Compressor Question

Reply #7 –
Following on from TurboJack clear description, to help diagnose, if a jumper wire on a pressure sensor starts the compressor, you found the cause and the compressor could run for a while to see if cools the dash evaporator.

We built a low-pressure sensor connector with a switch to force compressor to run when adding a refrigerant can sitting in a pan of hot water. But after finding a hose connection leak 7 years ago, we have not added any more refrigerant cans.

BTW, low and high pressure sensor switches can be located anywhere in the engine compartment, usually one on suction hose from condenser coil to compressor and the other on pressure hose out of compressor. I have also seen a single combination high/low pressure sensor.
 

SPLIT: Re: A/C Compressor Question

Reply #8 –
Axle discussion split from A/C discussion
Brett Wolfe
EX: 1993 U240
Moderator, ForeForum 2001-
Moderator Diesel RV Club 2002-
Moderator, FMCA Forum 2009-2020
Chairman FMCA Technical Advisory Committee 2011-2020